1. Technical Field
The present invention relates to an ink containing a functional layer forming material, an ink container, and a method for producing a functional element using the ink.
2. Related Art
There has been known a droplet ejection method (or also referred to as “inkjet method”) for forming, for example, a functional layer including a light-emitting layer disposed in a pixel of an organic electroluminescence (EL) device, or a colored layer of a color filter used in a liquid crystal display device using an inkjet head capable of ejecting a liquid body (ink) as a droplet.
In such a droplet ejection method, an applied film having a desired film thickness is required to be formed by reliably placing a droplet ejected from an inkjet head in a region which is divided by a partition wall and in which the applied film is formed.
For example, JP-A-2007-103381 (PTL 1) discloses an ink composition, which is applied by an inkjet method in the production of an organic EL element, contains a hole injection material or a light-emitting material, and has a viscosity of 1 to 20 mPa·s (sec), a surface tension of 20 to 70 mN/m, and a contact angle with a material constituting a nozzle surface of an inkjet head of 30 to 17° (degree). It is said that by using such an ink composition, the clogging of a nozzle hole and the flight curve of an ink droplet are suppressed, and also the ejection of an ink droplet is made smooth, and therefore, the ejection amount and the ejection timing can be controlled, and thus, stable ejection of an ink droplet can be realized.
However, even if the physical properties such as viscosity, surface tension, and contact angle of an ink composition are specified as disclosed in PTL 1, a droplet ejected from a nozzle of an inkjet head is not reliably placed in a region where an applied film is formed in some cases. For example, when a droplet is ejected by decreasing the ejection amount, the flight of the droplet is unstable or when a droplet is ejected by increasing the ejection amount, the droplet is ejected in a state of leaving a tail behind, and thus, there is a problem that the ejected droplet cannot be reliably landed in a desired region.